"Great Dying" Lasted 200,000 Years
By BRIAN HANDWERK - NATIONAL GEOGRAPHIC NEWS
Added: Mon, 28 Nov 2011 14:57:40 UTC
Long before the dinosaurs, a bleak environment of widespread fires and oxygen-poor coastal seawater killed off some 90 percent of all Earth's living species. The whole process took less than 200,000 years, according to a new study of the planet's most catastrophic mass-extinction event.
The end-Permian extinction probably isn't as well known as the Cretaceous extinction that wiped out the dinosaurs some 65 million years ago. But the end-Permian collapse nearly spelled the end of life on Earth.
Now scientists have painted a picture of just how fast the "Great Dying" unfolded 252 million years ago.
While the causes of the Permian extinction remain a mystery, from here on out, any theory must be compatible with a 200,000-year time frame centered around 252.28 million years ago, the authors assert. This time span is span indicated by analysis of fossils and chemical evidence of changes in Earth's carbon cycle in rocks from southern China to Tibet.
The two-millennia period is far shorter than the time span that has been widely accepted, according to study co-author Shu-zhong Shen, a paleontologist at the China's Nanjing Institute of Geology and Palaeontology.
The rock and fossil data show that the nightmare scenario for living species unfolded on land and sea simultaneously, said co-author Sam Bowring of the Massachusetts Institute of Technology (MIT).
As of now, Bowring said, "whatever mechanism you invoke [as the cause of the mass extinction] can't be purely marine or purely continental."
Wherever a life-form might have been during the Great Dying, the picture would have been anything but sunny, the researchers say.
"Widespread wildfires played an important role in the rapid deforestation at the end of Permian," said Nanjing's Shen, citing plentiful charcoal-rich and soot-bearing beds found in sedimentary rock of the period.
Rocks also provide hard evidence, via carbon isotope signatures, of oceans under stress as the carbon cycle was reorganized and oxygen levels fell during the Great Dying.
"Marine-organism fossils during the extinction period show a shift from normal species to those who could better tolerate low-oxygen waters," Shen said.
Also, "survivors of the extinction were smaller than the species that came before them—a phenomenon known as the Lilliput effect," after an island home to tiny humans in Gulliver's Travels. This shrinkage is partly attributable to the low oxygen levels, according to Shen.
MIT's Bowring added, "The beauty of those rocks is that we can see what's happening before the extinction event, during the extinction event, and after the extinction—and calibrate it all in absolute time."
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